1. Field of the Invention
This invention relates generally to X-ray apparatus, and more particularly to apparatus for centering an X-ray cassette in an X-ray beam adjusting X-ray cassette holder.
2. Description of the Prior Art
Film or other sensitive material exposed to X-rays for medical diagnostic purposes commonly is packaged in cassettes of varying sizes to suit particular purposes. Since the sensitive material area of a specific cassette should be exactly impinged by an X-ray beam, it is desirable to limit the size of the X-ray beam to substantially the exact size of the sensitive material in the cassette. Otherwise, a patient being X-rayed may be subjected to excessive radiation and potential health hazards, or the film or other sensitive material in the cassette may be inadvertently fogged and ruined for its purpose.
Although adjustment of the X-ray beam can be performed manually by an operator of the machine, it is preferable to have the X-ray beam automatically adjusted to conform to a particular cassette size. U.S. Pat. No. 3,764,808, issued Oct. 9, 1973, to R. R. Lackey, et al, discloses apparatus for this purpose. This device employs a pair of continuously variable transducers, such as rotary potentiometers, mounted on a cassette holder and engageable with a cassette in order to determine its size. One of the transducers employs a pair of jaws attached to a cable arrangement for centering a cassette in a first direction, while the other transducer is adjusted by a pivoted arm mounted on the cassette holder and disposed for contacting one side of a cassette centered between the aforementioned jaws. A problem encountered with this arrangement is that the cassette may not be centered in a second direction perpendicular to the first direction so as to give an erroneous reading to the other of the transducers, resulting in an improper reading of sides of a cassette mmounted on the holder.